Optimize, prepare for eventual sendheaders use, add sanity check

spvsvc/spvchain/blockmanager.go

@@ -131,6 +131,7 @@ type blockManager struct {
 	reorgList      *list.List
 	startHeader    *list.Element
 	nextCheckpoint *chaincfg.Checkpoint
+	lastRequested  chainhash.Hash
 
 	minRetargetTimespan int64 // target timespan / adjustment factor
 	maxRetargetTimespan int64 // target timespan * adjustment factor
@@ -604,11 +605,15 @@ func (b *blockManager) handleInvMsg(imsg *invMsg) {
 	// If this is the sync peer or we're current, get the headers
 	// for the announced blocks and update the last announced block.
 	if lastBlock != -1 && (imsg.peer == b.syncPeer || b.current()) {
-		// Make a locator starting from the latest known header we've
+		lastHash := b.headerList.Back().Value.(*headerNode).header.BlockHash()
-		// processed.
+		// Only send getheaders if we don't already know about the last
+		// block hash being announced.
+		if lastHash != invVects[lastBlock].Hash &&
+			b.lastRequested != invVects[lastBlock].Hash {
+			// Make a locator starting from the latest known header
+			// we've processed.
 			locator := make(blockchain.BlockLocator, 0,
 				wire.MaxBlockLocatorsPerMsg)
-		lastHash := b.headerList.Back().Value.(*headerNode).header.BlockHash()
 			locator = append(locator, &lastHash)
 			// Add locator from the database as backup.
 			knownLocator, err := b.server.LatestBlockLocator()
@@ -616,7 +621,15 @@ func (b *blockManager) handleInvMsg(imsg *invMsg) {
 				locator = append(locator, knownLocator...)
 			}
 			// Get headers based on locator.
-		imsg.peer.PushGetHeadersMsg(locator, &invVects[lastBlock].Hash)
+			err = imsg.peer.PushGetHeadersMsg(locator,
+				&invVects[lastBlock].Hash)
+			if err != nil {
+				log.Warnf("Failed to send getheaders message "+
+					"to peer %s: %s", imsg.peer.Addr(), err)
+				return
+			}
+			b.lastRequested = invVects[lastBlock].Hash
+		}
 	}
 }
 
@@ -716,6 +729,12 @@ func (b *blockManager) handleHeadersMsg(hmsg *headersMsg) {
 			if hmsg.peer != b.syncPeer && !b.current() {
 				return
 			}
+			// Check if this is the last block we know of. This is
+			// a shortcut for sendheaders so that each redundant
+			// header doesn't cause a disk read.
+			if blockHash == prevHash {
+				continue
+			}
 			// Check if this block is known. If so, we continue to
 			// the next one.
 			_, _, err := b.server.GetBlockByHash(blockHash)
@@ -764,7 +783,7 @@ func (b *blockManager) handleHeadersMsg(hmsg *headersMsg) {
 				height: int32(backHeight),
 			})
 			totalWork := big.NewInt(0)
-			for _, reorgHeader := range msg.Headers[i:] {
+			for j, reorgHeader := range msg.Headers[i:] {
 				err = b.checkHeaderSanity(reorgHeader,
 					maxTimestamp, true)
 				if err != nil {
@@ -776,6 +795,10 @@ func (b *blockManager) handleHeadersMsg(hmsg *headersMsg) {
 				}
 				totalWork.Add(totalWork,
 					blockchain.CalcWork(reorgHeader.Bits))
+				b.reorgList.PushBack(&headerNode{
+					header: reorgHeader,
+					height: int32(backHeight+1) + int32(j),
+				})
 			}
 			log.Tracef("Sane reorg attempted. Total work from "+
 				"reorg chain: %v", totalWork)
@@ -808,13 +831,18 @@ func (b *blockManager) handleHeadersMsg(hmsg *headersMsg) {
 			log.Tracef("Total work from known chain: %v", knownWork)
 			// Compare the two work totals and reject the new chain
 			// if it doesn't have more work than the previously
-			// known chain.
+			// known chain. Disconnect if it's actually less than
-			if knownWork.Cmp(totalWork) >= 0 {
+			// the known chain.
-				log.Warnf("Reorg attempt that does not have "+
+			switch knownWork.Cmp(totalWork) {
-					"more work than known chain from peer "+
+			case 1:
-					"%s -- disconnecting", hmsg.peer.Addr())
+				log.Warnf("Reorg attempt that has less work "+
+					"than known chain from peer %s -- "+
+					"disconnecting", hmsg.peer.Addr())
 				hmsg.peer.Disconnect()
+				fallthrough
+			case 0:
 				return
+			default:
 			}
 			// At this point, we have a valid reorg, so we roll
 			// back the existing chain and add the new block header.
@@ -884,8 +912,9 @@ func (b *blockManager) handleHeadersMsg(hmsg *headersMsg) {
 		//return
 	}
 
-	// Request the next batch of headers starting from the latest known
+	// If not current, request the next batch of headers starting from the
-	// header and ending with the next checkpoint.
+	// latest known header and ending with the next checkpoint.
+	if !b.current() {
 		locator := blockchain.BlockLocator([]*chainhash.Hash{finalHash})
 		nextHash := zeroHash
 		if b.nextCheckpoint != nil {
@@ -897,6 +926,7 @@ func (b *blockManager) handleHeadersMsg(hmsg *headersMsg) {
 				"peer %s: %s", hmsg.peer.Addr(), err)
 			return
 		}
+	}
 }
 
 // checkHeaderSanity checks the PoW, and timestamp of a block header.

spvsvc/spvchain/db.go

@@ -292,6 +292,36 @@ func LatestBlock(tx walletdb.Tx) (wire.BlockHeader, uint32, error) {
 	return header, height, nil
 }
 
+// CheckConnectivity cycles through all of the block headers, from last to
+// first, and makes sure they all connect to each other.
+func CheckConnectivity(tx walletdb.Tx) error {
+	header, height, err := LatestBlock(tx)
+	if err != nil {
+		return fmt.Errorf("Couldn't retrieve latest block: %s", err)
+	}
+	for height > 0 {
+		newheader, newheight, err := GetBlockByHash(tx,
+			header.PrevBlock)
+		if err != nil {
+			return fmt.Errorf("Couldn't retrieve block %s: %s",
+				header.PrevBlock, err)
+		}
+		if newheader.BlockHash() != header.PrevBlock {
+			return fmt.Errorf("Block %s doesn't match block %s's "+
+				"PrevBlock (%s)", newheader.BlockHash(),
+				header.BlockHash(), header.PrevBlock)
+		}
+		if newheight != height-1 {
+			return fmt.Errorf("Block %s doesn't have correct "+
+				"height: want %d, got %d",
+				newheader.BlockHash(), height-1, newheight)
+		}
+		header = newheader
+		height = newheight
+	}
+	return nil
+}
+
 // BlockLocatorFromHash returns a block locator based on the provided hash.
 func BlockLocatorFromHash(tx walletdb.Tx, hash chainhash.Hash) blockchain.BlockLocator {
 	locator := make(blockchain.BlockLocator, 0, wire.MaxBlockLocatorsPerMsg)

spvsvc/spvchain/spvchain.go

@@ -212,6 +212,23 @@ func (sp *serverPeer) pushGetCFHeadersMsg(locator blockchain.BlockLocator,
 	return nil
 }
 
+// pushSendHeadersMsg sends a sendheaders message to the connected peer.
+func (sp *serverPeer) pushSendHeadersMsg() error {
+	if sp.VersionKnown() {
+		if sp.ProtocolVersion() > wire.SendHeadersVersion {
+			sp.QueueMessage(wire.NewMsgSendHeaders(), nil)
+		}
+	}
+	return nil
+}
+
+// OnVerAck is invoked when a peer receives a verack bitcoin message and is used
+// to send the "sendheaders" command to peers that are of a sufficienty new
+// protocol version.
+func (sp *serverPeer) OnVerAck(_ *peer.Peer, msg *wire.MsgVerAck) {
+	sp.pushSendHeadersMsg()
+}
+
 // OnVersion is invoked when a peer receives a version bitcoin message
 // and is used to negotiate the protocol version details as well as kick start
 // the communications.
@@ -1058,6 +1075,7 @@ func newPeerConfig(sp *serverPeer) *peer.Config {
 	return &peer.Config{
 		Listeners: peer.MessageListeners{
 			OnVersion: sp.OnVersion,
+			//OnVerAck:    sp.OnVerAck, // Don't use sendheaders yet
 			OnBlock:     sp.OnBlock,
 			OnInv:       sp.OnInv,
 			OnHeaders:   sp.OnHeaders,